The present invention relates to a method and a device for controlling fuel metering in an internal combustion engine.
In known pump-nozzle units, only one final controlling element is provided, in particular a solenoid valve or a piezoelectric actuator, which may be energized or de-energized. This corresponds to the two states xe2x80x9coffxe2x80x9d and xe2x80x9cinjection.xe2x80x9d More recent pump-nozzle systems have a third additional state, in which pressure is built up in the pump and is thus variably adjustable. In other words, the pressure at which injection starts is variably adjustable. This provides an additional free, continuous parameter, which has considerable influence on the injected amount.
Such fuel injection units contain a first final controlling element which receives a first trigger signal, which controls the start and end of fuel metering, and a second final controlling element which receives a second trigger signal, which controls the pressure that is available for fuel metering. Such a fuel injection unit is known from European Published Patent Application No. 840 003, for example.
According to the present invention, variation over time of the injection pressure and thus of the injected amount is controlled using a semi-empirical model on the basis of the first and second trigger signals using constants and relationships between the variables.
It is particularly advantageous the variation of pressure in a method and a device for determining a fuel pressure and/or an injected amount of fuel on the basis of at least a first trigger signal and a second trigger signal. This is particularly advantageous in the case of a fuel injection unit which meters fuel to an internal combustion engine as a function of a first and a second trigger signal, the first trigger signal controlling the start and the end of fuel metering and the second trigger signal controlling the pressure buildup.
It is particularly advantageous if variables which characterize the start of pressure buildup, the start of fuel metering and/or the end of fuel metering are predefinable on the basis of the first and second trigger signals. These variables essentially characterize the variation of fuel pressure over time.
In addition to the above-named variables, the rotational speed essentially determines the variation of pressure. This is the case in particular in pump-nozzle systems. Therefore, the rotational speed is very advantageously used additionally for determining the variation of pressure.
The injected amount of fuel is determined on the basis of the variation of pressure by integration in a simple manner.
It is particularly advantageous that the computed amount of fuel and/or the computed pressure is compared with predefined values, and a malfunction is detected on the basis of the comparison. This provides simple and effective monitoring of the injection device.
It is particularly advantageous and simple if the computed amount of fuel is compared with a desired amount of fuel, and a malfunction is detected on the basis of the comparison.
In using the model as a pressure estimator, the pressure and the injected fuel amount are continuously computed in the controller. The pressure signal or fuel amount signal thus obtained may then be used for malfunction monitoring and/or control of the injection. In particular, it may be provided that a malfunction is detected if the pressure exceeds a maximum pressure or the injected amount exceeds a maximum amount.
Furthermore, the model may be used as a calibration aid. The injected amount in these systems is essentially a function of the needle opening pressure in addition to the duration of injection. Thus, two parameters are established by the calibrator for setting the desired amount at a given rotational speed.
The formulas on which the model is based are invertible. This allows the calibrator to specify the variation of injection, i.e., amount, start of injection, and needle opening pressure. The injection sequence is computed from these variables.
Implementations in the form of a computer program having a program code and in the form of a computer program product having a program code are of particular significance. The computer program according to the present invention has a program code for executing all steps of the method according to the present invention when the program is executed on a computer, in particular a controller for an internal combustion engine. In this case, the present invention is implemented by a program stored in the controller, so that this controller provided with the program represents the present invention just as does the method for whose execution the program is suitable. The computer program product according to the present invention has a program code stored on a computer-readable data medium for executing the method according to the present invention when the program product is executed on a computer, in particular a controller for an internal combustion engine of a motor vehicle. In this case, the present invention is therefore implemented by a data medium, so that the method according to the present invention is executable if the program product, i.e., the data medium, is integrated in a controller for an internal combustion engine, in particular of a motor vehicle. An electrical storage medium such as a read-only memory (ROM), an EPROM, or a permanent electric memory such as a CD-ROM or DVD, may be used in particular as a data medium, i.e., as a computer program product.